Knowing correct amount of overview levels for raster?

Question

I'm working with large rasters which require overviews in order to be browsed efficiently. I'm successful in creating overviews, external in my case (.ovr), but I haven't found a source about figuring out the correct amount of overview levels for a raster. I'm looking either for an automatic way or a formula with which one could deduce the right amount of them.

Right now I'm creating external overviews, then checking out if amount of specified levels was enough in QGIS and finally rerun gdaladdo if it wasn't. An example of gdaladdo syntax I'm using:

gdaladdo raster.tif 2 4 8 16 32 64 128 256 1024 2048 -r average -ro --config COMPRESS_OVERVIEW 
JPEG --config PHOTOMETRIC_OVERVIEW YCBCR --config INTERLEAVE_OVERVIEW PIXEL

Does anyone have any tips?

Answer 1

Since June 28th, 2017 you do not really need to bother about the explicit levels if you are fine with the power of two levels. See the announcement in gdal-dev mailing list https://lists.osgeo.org/pipermail/gdal-dev/2017-June/046820.html

Default levels are also documented in the manual https://www.gdal.org/gdaladdo.html

levels: A list of integral overview levels to build. Ignored with -clean option. Starting with GDAL 2.3, levels are no longer required to build overviews. In which case, appropriate overview power-of-two factors will be selected until the smallest overview is smaller than the value of the -minsize switch.

-minsize val: (starting with GDAL 2.3) Maximum width or height of the smallest overview level. Only taken into account if explicit levels are not specified. Defaults to 256.